Tokyo and Okinawa are set to return to the courts Friday after the central government said it will sue the Okinawa Prefectural Government over its failure to cooperate on relocating a U.S. military base, Chief Cabinet Secretary Yoshihide Suga said Thursday.

The lawsuit will recommence a bitter legal to-and-fro over the relocation of Marine Corps Air Station Futenma from Ginowan to the Henoko area of Nago in the prefecture.

In March, the two sides accepted out-of-court mediation by the Naha branch of the Fukuoka District Court, which urged them to stop squabbling and talk. Each withdrew its lawsuits against each other.

The settlement required them to await a final ruling by an arbitration panel under the internal affairs ministry. That ruling can be contested in court, but the court's decision would be final, according the mediation agreement.

However, the panel issued its judgment in June with no clear conclusion. It merely urged them to keep talking.

The lawsuit that the central government will file Friday will be based on that March settlement, Suga said.

"The agreement is still effective," Suga told a news conference. "We will follow a final decision at the court. At the same time, we will also continue talks with Okinawa."

Suga met with Okinawa Gov. Takeshi Onaga in Tokyo earlier in the day and notified him of the central government's decision.

It was not well received. A fresh lawsuit would be "extremely deplorable," Onaga told reporters afterward.

Onaga opposes relocation, saying it will only strengthen the U.S. military presence in the prefecture and further increase the burden on residents.

Futenma is located in the middle of Ginowan, an urban area where residents say their lives are blighted by noise pollution and that they live in fear of aviation accidents.

Tokyo and Washington agreed to remove the Futenma base in 1996 and chose Henoko as the relocation site in 1999. But the project has been long stalled due to opposition from locals.

Okinawa saw fierce ground battles in the closing days of World War II, and anti-military sentiment remains strong. It is thought that most Okinawa voters support Onaga on Futenma.

Prime Minister Shinzo Abe has pushed for relocation, calling it essential to the Japan-U.S. military alliance.

Friday's lawsuit is expected to center on the fact that Onaga revoked permission for landfill work at Henoko, the site where runways will extend off the coast to accommodate Marine Corps aircraft.

The central government will ask the Naha branch of the Fukuoka High Court to declare Onaga in breach of his legal obligations because he has failed to retract that revocation.

Following the June adjudication, Okinawa Prefecture said it would not file a fresh lawsuit against the central government.

Onaga may now review that position. "We will consider what to do as soon as we receive the complaint," he said Thursday.